The ability to duplicate and store the contents of a storage device is an important feature of a storage system. Data may be stored in parallel to safeguard against the failure of a single storage device or medium. Upon a failure of the first storage device or medium, the system may then retrieve a copy of the data contained in a second storage device or medium. The ability to duplicate and store the contents of the storage device also facilitates the creation of a fixed record of contents at the time of duplication. This feature allows users to recover a prior version of inadvertently edited or erased data.
There are space and processing costs associated with copying and storing the contents of a storage device. For example, some storage devices cannot accept input/output (I/O) operations while its contents are being copied. Furthermore, the storage space used to keep the copy cannot be used for other storage needs.
Storage systems and storage software products can provide ways to make point-in-time copies of disk volumes, sometimes referred to as snapshots. In some of these systems and products, copies may be made quickly, without significantly disturbing applications using disk volumes. In other products, copies may be made space efficient by sharing storage instead of copying all the disk volume data.
Periodically, there may be a need to restore one or more volumes of a storage system to a data state that represents a previous point in time. Users or administrators of storage systems may have varying goals for restore processes. In some instances, restore operations that enable contemporaneous access to data may find utility.